This invention is in the field of glass fiber reinforced polyethylene terephthalate molding compounds.
Polyethylene terephthalate molding compounds which are reinforced with glass fibers, asbestos fibers, or other fibrous mineral material are known to either crystallize slowly and give a resin rich surface which gives a good surface finish but inferior mechanical properties and slow molding cycles, or rapidly crystallize, giving good mechanical properties and short molding cycles but leave a filler (glass) rich surface which has low gloss. One method of improving surface finish is to increase the mold temperature but this can result in longer cooling times. It is also known that molding undried polyethylene terephthalate produces parts with good gloss but poor mechanical properties.
It is difficult to get fiber reinforced polyethylene terephthalate molding compounds to display a combination of optimized surface finish characteristics, rapid crystallization, and acceptably high, from a commercial viewpoint, thermal and mechanical properties. Processability, shorter cycle times and better flow properties are important. Thus, even when a particular polyethylene terephthalate molding compound displays both good surface finish characteristics and, after injection molding, some good strength characteristics, it may not be suitable for use in many molding resin compound applications, because it does not also possess other commercially required characteristics. For example, for use in so called engineering resin applications, a glass fiber reinforced polyethylene terephthalate molding compound needs to have attractive surface appearance, good spiral flow, rapid crystallization, high heat distortion temperature, and an ability to produce a molded part which has a smooth, glossy surface and minimal warpage after the part is removed from a mold.
There is a need for reinforced polyethylene terephthalate molding compounds with high surface gloss which also have engineering resin performance characteristics. Also, there is a need for compounds of this type which display high flow rates under molding conditions without water addition and without lubricant addition. In addition, these compounds should also be capable of having a flame retardant material added thereto in an amount effective for achieving flame retardancy without a significant or commercially unacceptable loss of properties.